Opening, registering and marking the Top 8 pools
I'll just repeat something that Andy and I have both posted … but not for a long, long time:
Absolutely, do NOT do that for your events. Always let the players crack the packs.
I do like your idea of having a couple pre-registered pools for late arrivals. I woild recommend only using these for players who arrive during registration; that way they still have to swap, and you aren't seen as handing them a really good pool (or bad!), so no perception of favoritism.
If you have players arrive after the swap, let them crack fresh packs, monitor their registration and deck building, and give them the round one loss for Tardiness.